1. Field of the Invention
The subject invention is directed to an apparatus to compensate for differential growth of fuel injector components due to thermal expansion, and more particularly, to an apparatus for accommodating thermal growth of a fuel injector body relative to a fuel delivery tube disposed within the fuel injector body during engine operation.
2. Description of Related Art
Fuel injectors are important components of gas turbine engines and they play a critical role in determining engine performance. A typical fuel injector includes an external support body having an inlet fitting at one end for receiving fuel and an atomizer nozzle at the other end for issuing atomized fuel into the combustor of a gas turbine engine. The inlet fitting is in fluid communication with the atomizer nozzle by way of an internal fuel delivery tube.
During engine operation, the external support body of the fuel injector is surrounded by high-temperature compressor air, while the internal fuel delivery tube carries liquid fuel to the atomizer nozzle at a much lower temperature than the compressor air. Because of the temperature difference, the injector support body experiences thermal expansion differently than the fuel delivery tube. More specifically, the injector support body will experience thermal growth to a greater extent than the fuel delivery tube.
In some fuel injectors, the fuel delivery tubes are rigidly connected to the injector support body at one end adjacent the inlet fitting and to the atomizer nozzle on the other end, using a welded or brazed joint. As a result of the differential thermal expansion between the injector support and the fuel delivery tube, high stress concentrations can develop at the joint locations. These stress concentrations can lead to the formation and propagation of cracks, eventually leading to fuel leaks, resulting in injector failures.
Efforts have been made to mitigate these problems. For example, for many years it was well known to design injectors with fuel tubes having helical or coiled sections to accommodate differential thermal growth between the injector support and the fuel tube. Indeed, the prior art is replete with patents disclosing such coiled fuel tubes, as shown for example in U.S. Pat. No. 3,129,891 to Vdoviak; U.S. Pat. No. 4,258,544 to Gebhart et al.; U.S. Pat. No. 4,649,950 to Bradley et al.; and U.S. Pat. No. 6,276,141 to Pelletier. Those skilled in the art will readily appreciate that there is a significant cost associated with the formation of a helically coiled fuel tube, particularly in instances wherein dual concentric fuel tubes are employed, as in the Pelletier patent.
The subject invention provides a cost-effective solution to mitigate the problems associated with differential thermal expansion of injector components, and an improvement over prior art devices employing helical fuel tubes. More particularly, the subject invention provides an apparatus to compensate for thermal growth of the injector support body relative to the fuel delivery tube during engine operation.